Study on infestation levels and spatial distributions of Amaranthus blitoides, Chenopodium album and Solanum nigrum in corn field

For increasing the effectiveness of weed management and more understanding of weed population dynamics, spatial distribution needs to more attentions. Infestation levels and spatial distributions of Amaranthus blitoides, Chenopodium album and Solanum nigrum were studied in four 10x30 m corn fields. N-fertilizer was applied in two method of whole application at the time of corn planting (T1 and T2) and equal split application at the time of corn planting and at six-leaf stage (T3 and T4). One of either fields with the same method of N-fertilizer application, received herbicide too (T1 and T3). Weeds Samples were taken four times at the intersection of 2.5m square grids with 23days interval. The first sample was taken June 24, before top-dressing and herbicide application in related plots. For studying weed spatial distribution, the parameters of appropriate semivariogram model were calculated and weed contour maps were constructed by using kriging. The weed semivariograms fitted spherical and exponential models, over four sampling times and fields and spatial autocorrelation during growing season, was moderate to strong. In early growing season, Amaranthus blitoides was the dominant weed species in all fields, but lower density was recorded for Chenopodium album and Solanum nigrum. At the first sampling time, mean density of A. blitoides and S. nigrum in fields with split application of N-fertilizer was respectively more- and less than fields with whole application of N-fertilizer. In the case of C. album an evident difference wasn’t observed. Herbicide application in related plots considerably reduced the density of three mentioned species; however density never became zero. In the majority of cases the lack of herbicide application causes to increase in population density at the second sampling time. Spatial structure was observed in all three species and study on contour maps confirmed the existence of patches that the density was high in their center, but decreasing gradually toward edges. In general, despite of some displacement, structure and location of patches were kept and possibly these places were the locations for weed emergence in next year. So site-specific herbicide application and exploitation of its advantages may be possible; however, more researches are necessary. Keywords: Population dynamics, weed mapping, site-specific application, 2,4-D+MCPA, nitrogen

Effect of nitrogen amount, time and 2,4-D+MCPA application on spatial distribution of lambsquarters seed bank in a corn field

In order to evaluate the effect of nitrogen and herbicide management on distribution patterns of lambsquarters seed bank, an experiment was conducted in a grain corn field at the Agricultural Research Station, Ferdowsi University of Mashhad 2006 growing season.Treatments consisted of application of: 25 kg/ha nitrogen fertilizer at the time of corn planting with 2,4-D+MCPA herbicide(533 g. ai./ha 2.4.D+467 g. ai./ha MCPA), 25 kg/ha nitrogen fertilizer at the time of corn planting without herbicide, 25 kg/ha nitrogen fertilizer at the time of corn planting and six-leaf stage with herbicide, 25 kg/ha nitrogen fertilizer at the time of corn planting and six-leaf stage without herbicide, 120 kg/ha nitrogen fertilizer at the time of corn planting with herbicide, 120 kg/ha nitrogen fertilizer at the time of corn planting without herbicide 120 kg/ha nitrogen fertilizer at the time of corn planting and six-leaf stage with herbicide and 120 kg/ha nitrogen fertilizer at the time of corn planting and six-leaf stage without herbicide. Application of herbicide was useful in reducing the amount of lambsquaters seed bank. Semivariograms of seeds were fitted with spherical and exponential models.Semivariogram analysis in the levels of treatments indicated a range of influence of 0.88m to 45.12 m . The highest spatial correlation was 0.093% and the lowest was 28.81%. Weed seed bank patches was obvious in maps. Although the nitrogen fertilizer had no strong effect on reducing the amount of seed bank , the application of 2,4-D+MCPA was a useful practice in reducing weed seed bank